Trabecular Structure Parameters Research Articles

Additive effects from a combined treatment using parathyroid hormone and ibandronate in the ovariectomized rat

Additive effects from a combined treatment using parathyroid hormone and ibandronate in the ovariectomized rat

E-modulus mapping at bone packet level: Combination of scanning acoustic microscopy in time of flight mode and back scattered electron imaging

E-modulus mapping at bone packet level: Combination of scanning acoustic microscopy in time of flight mode and back scattered electron imaging

Interferon-γ plays a role in bone formation in vivo and rescues osteoporosis in ovariectomized mice

Interferon γ (IFN-γ) is a cytokine produced locally in the bone microenvironment by cells of immune origin as well as mesenchymal stem cells. However, its role in normal bone remodeling is still poorly understood. In this study we first examined the consequences of IFN-γ ablation in vivo in C57BL/6 mice expressing the IFN-γ receptor knockout phenotype (IFNγR1(-/-)). Compared with their wild-type littermates (IFNγR1(+/+)), IFNγR1(-/-) mice exhibit a reduction in bone volume associated with significant changes in cortical and trabecular structural parameters characteristic of an osteoporotic phenotype. Bone histomorphometry of IFNγR1(-/-) mice showed a low-bone-turnover pattern with a decrease in bone formation, a significant reduction in osteoblast and osteoclast numbers, and a reduction in circulating levels of bone-formation and bone-resorption markers. Furthermore, administration of IFN-γ (2000 and 10,000 units) to wild-type C57BL/6 sham-operated (SHAM) and ovariectomized (OVX) female mice significantly improved bone mass and microarchitecture, mechanical properties of bone, and the ratio between bone formation and bone resorption in SHAM mice and rescued osteoporosis in OVX mice. These data therefore support an important physiologic role for IFN-γ signaling as a potential new anabolic therapeutic target for osteoporosis.

Breast tumors induced by N-methyl-N-nitrosourea are damaging to bone strength, structure, and mineralization in the absence of metastasis in rats

Current theory on the influence of breast cancer on bone describes metastasis of tumor cells to bone tissue, followed by induction of osteoclasts and bone degradation. Tumor influences on bone health in pre- or nonmetastatic models are unknown. Female rats (n = 48, 52 days old) were injected with N-methyl-N-nitrosourea (MNU) to induce breast cancer. Animals were euthanized 10 weeks later, and tumors were weighed and classified histologically. Right femurs were extracted for testing of bone mineral density (BMD) by dual X-ray absorptiometry (DXA), bone mechanical strength by three-point bending and femoral neck bending tests, and structure by micro-computed tomography (µCT). Of 48 rats, 22 developed one or more tumors in response to MNU injection by 10 weeks. Presence of any tumor predicted significantly poorer bone health in 17 of 28 measures. In tumored versus nontumored animals, BMD was adversely affected by 3%, force at failure of the femoral midshaft by 4%, force at failure of the femoral neck by 12%, and various trabecular structural parameters by 6% to 27% (all p < .05). Similarly, greater tumor burden, represented by total tumor weight, adversely correlated with bone outcomes: r = -0.51 for BMD, -0.42 and -0.35 for femur midshaft force and work at failure, and between 0.36 and 0.59 (absolute values) for trabecular architecture (all p < .05). Presence of MNU-induced tumors and total tumor burden showed a negative association with bone health of the femur in rats in the absence of metastasis. Further study is required to elucidate mechanisms for this association.

Association between condylar morphology and changes in bony microstructure and sub-synovial inflammation in experimental temporomandibular joint arthritis

In juvenile idiopathic arthritis involvement of the temporomandibular joints (TMJs) is often associated with mandibular growth deviations. The relation between the growth deviations and severity of the inflammation, condylar shape, the micro-architecture, and the quality of the bone has not previously been investigated. This paper studies the effect on the bony structures in mandibular condylar development in rabbits with antigen-induced arthritis. Included were 42 juvenile rabbits with ovalbumin-induced arthritis of the TMJs treated with intraarticular saline, intraarticular etanercept or subcutaneous etanercept. A TMJ from each animal was scanned using micro-computed tomography and structural parameters were calculated. Three-dimensional reconstructions of the mandibular condyle were scored blindly as normal or abnormal. TMJs were stratified for condylar morphology and were evaluated against data on trabecular structural parameters, inflammation, degree of mineralization, overall mandibular growth, and mineral apposition rate. Abnormal morphology were seen in 15/32 animals available for data analysis. Erosions were an uncommon finding. Abnormal morphology was strongly related to the degree of inflammation. The trabecular separation was larger in group with abnormal morphology than in the group with normal morphology. Abnormal condylar morphology was not associated with overall mandibular growth. No differences were observed in mineral apposition rate. No differences in structural parameters were seen according to treatment modality. We showed that severe inflammation in the TMJs during mandibular development was associated with morphological changes in the mandibular condyle. These changes were predominantly seen at the macro-morphological level and only very few differences were structural.

Automated 3D trabecular bone structure analysis of the proximal femur—prediction of biomechanical strength by CT and DXA

SummaryThe standard diagnostic technique for assessing osteoporosis is dual X-ray absorptiometry (DXA) measuring bone mass parameters. In this study, a combination of DXA and trabecular structure parameters (acquired by computed tomography [CT]) most accurately predicted the biomechanical strength of the proximal femur and allowed for a better prediction than DXA alone.IntroductionAn automated 3D segmentation algorithm was applied to determine specific structure parameters of the trabecular bone in CT images of the proximal femur. This was done to evaluate the ability of these parameters for predicting biomechanical femoral bone strength in comparison with bone mineral content (BMC) and bone mineral density (BMD) acquired by DXA as standard diagnostic technique.MethodsOne hundred eighty-seven proximal femur specimens were harvested from formalin-fixed human cadavers. BMC and BMD were determined by DXA. Structure parameters of the trabecular bone (i.e., morphometry, fuzzy logic, Minkowski functionals, and the scaling index method [SIM]) were computed from CT images. Absolute femoral bone strength was assessed with a biomechanical side-impact test measuring failure load (FL). Adjusted FL parameters for appraisal of relative bone strength were calculated by dividing FL by influencing variables such as body height, weight, or femoral head diameter.ResultsThe best single parameter predicting FL and adjusted FL parameters was apparent trabecular separation (morphometry) or DXA-derived BMC or BMD with correlations up to r = 0.802. In combination with DXA, structure parameters (most notably the SIM and morphometry) added in linear regression models significant information in predicting FL and all adjusted FL parameters (up to R adj = 0.872) and allowed for a significant better prediction than DXA alone.ConclusionA combination of bone mass (DXA) and structure parameters of the trabecular bone (linear and nonlinear, global and local) most accurately predicted absolute and relative femoral bone strength.

Does Exercise Modify the Effects of Zoledronic Acid on Bone Mass, Microarchitecture, Biomechanics, and Turnover in Ovariectomized Rats?

Regular activity has effects on bone size, shape, and density, resulting in an increase in mechanical strength. The mechanism of action that underlies this improvement in bone strength is mainly linked to an increase in bone formation. Zoledronic acid (Z), in contrast, may prevent bone strength changes in ovariectomized (OVX) rodents by its potent antiresorptive effects. Based on these assumptions we hypothesized that combined effects of exercise (E) and Z may produce higher benefits on bone changes resulting from estrogen deficiency than either intervention alone. At 6 months of age, 60 female Wistar rats were OVX or sham operated (SH) and divided into five groups: SH, OVX, OVX-E, OVX-Z, and OVX-ZE. OVX rats were treated with a single IV injection of Z (20 microg/kg) or vehicle and submitted or not to treadmill exercise (15 m/min, 60 min/day, 5 days/week) for 12 weeks. Whole-body BMD and bone turnover markers were analyzed longitudinally. At sacrifice, femurs were removed. BMD by DXA, three-point bending test, and microCT were performed to study biomechanical and trabecular structure parameters, respectively. After 12 weeks, bone volume fraction decreased in OVX rats, whereas bone turnover rate, trabecular spacing, and structure model index increased compared with those in the SH group (P < 0.05). Zoledronic acid prevented the ovariectomy-induced trabecular bone loss and its subsequent trabecular microarchitectural deterioration. Treadmill exercise running was shown to preserve the bone strength and to induce bone turnover changes in favor of bone formation. However, the combined effects of zoledronic acid and running exercise applied simultaneously did not produce any synergetic or additive effects.

Reproducibility of trabecular structure analysis using flat-panel volume computed tomography

To determine inter-scan, inter-reader and intra-reader variability of trabecular structure analysis using flat-panel volume computed tomography (fp-VCT) in cadaver knee specimens. Five explanted knee specimens were imaged at three different time points using fp-VCT. Four parameters that quantify trabecular bone structure of the proximal tibia were measured by two observers at two different time points. Bland-Altman analysis was used to compute the inter-scan, inter-observer and intra-observer variability. Inter-scan variability was low, with a mean difference of 0% and a standard deviation less than 8.4% for each of the four parameters. The inter-observer and intra-observer variability was less than 2.8% +/- 8.5%. Fp-VCT is a method for assessing trabecular structure parameters with low inter-scan, inter-reader and intra-reader variability.

Assessment of trabecular bone structure of the calcaneus using multi-detector CT: Correlation with microCT and biomechanical testing

The prediction of bone strength can be improved when determining bone mineral density (BMD) in combination with measures of trabecular microarchitecture. The goal of this study was to assess parameters of trabecular bone structure and texture of the calcaneus by clinical multi-detector row computed tomography (MDCT) in an experimental in situ setup and to correlate these parameters with microCT (μCT) and biomechanical testing. Thirty calcanei in 15 intact cadavers were scanned using three different protocols on a 64-slice MDCT scanner with an in-plane pixel size of 208 μm and 500 μm slice thickness. Bone cores were harvested from each specimen and μCT images with a voxel size of 16 μm were obtained. After image coregistration, trabecular bone structure and texture were evaluated in identical regions on the MDCT images. After data acquisition, uniaxial compression testing was performed. Significant correlations between MDCT- and μCT-derived measures of bone volume fraction (BV/TV), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) were found (range, R2=0.19–0.65, p<0.01 or 0.05). The MDCT-derived parameters of volumetric BMD, app. BV/TV, app. Tb.Th and app. Tb.Sp were capable of predicting 60%, 63%, 53% and 25% of the variation in bone strength (p<0.01). When combining those measures with one additional texture index (either GLCM, TOGLCM or MF.euler), prediction of mechanical competence was significantly improved to 86%, 85%, 71% and 63% (p<0.01). In conclusion, this study showed the feasibility of trabecular microarchitecture assessment using MDCT in an experimental setup simulating the clinical situation. Multivariate models of BMD or structural parameters combined with texture indices improved prediction of bone strength significantly and might provide more reliable estimates of fracture risk in patients.

Influence of prednisolone-induced osteoporosis on bone mass and bone quality of the mandible in rats

The aim of this study was to clarify the effects of steroid treatment on the mandible. We divided 24 male Fisher rats, aged 10 weeks, into 2 groups: a control group (n = 11) and a prednisolone (Pred) treatment group (n = 13). The dose for the Pred group was 40 mg kg(-1) and was administered orally three times per week for 8 weeks. At the end of the experiment, we measured bone mass, bone strength and trabecular structure of the mandible and femur. Pred treatment decreased cortical bone mineral content (BMC), cortical thickness, stress/strain index and tissue volume of the mandible. However, there were no marked changes in trabecular structure parameters. A strong correlation was seen between mandibular and femoral cortical BMC (r = 0.71). These findings suggest that steroid treatment decreases the cortical BMC, bone area and bone strength of the mandible.

Analysis of Trabecular Bone Structure with Multidetector Spiral Computed Tomography in a Simulated Soft-Tissue Environment

We investigated the influence of soft tissue (ST) on image quality by high-resolution multidetector computed tomography (MDCT) scans and assessed the effect of surrounding ST on the quantification of trabecular bone structure. Eight bone cores obtained from human proximal femoral heads discarded during hip replacement surgery were scanned with micro-computed tomography (microCT) as well as with MDCT both without (w/o) and with (w) simulated surrounding ST, where a phantom imitated a human torso. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured in all scans. Apparent trabecular bone structure parameters were calculated and compared to similar parameters obtained in coregistered sections of the microCT scans. Residual errors were calculated as root-mean-square (RMS) errors relative to the microCT measurements. Compared to microCT results, trabecular structure parameters were overestimated by MDCT both w and w/o ST. SNR and CNR were significantly higher in the scans w/o ST. Significant correlations between microCT and MDCT results were found for bone fraction (r = 0.90 w/o ST, r = 0.84 w ST), trabecular number, and separation. RMS ranged from 10% to 15% for MDCT w/o ST and from 10% to 17% for MDCT w ST. Only bone fraction showed significantly different RMS and correlations for scans w/o vs. w ST (P < 0.05). This study showed that MDCT is able to visualize trabecular bone structure in an in vivo-like setting at skeletal sites within the torso such as the proximal femur. Even though ST scatter compromises image quality substantially, the major characteristics of the trabecular network can still be appreciated and quantified.

Severe Alterations of Bone Mass and Bone Structure after Allogeneic Stem Cell Transplantation: An Osteopathologic Analysis.

Prolonged survival after allogeneic SCT has led to an increased awareness of late complications in these patients. Loss of bone density after SCT has been reported in radiologic analyses (Ebeling 1999, Schulte 2000, Massenkeil 2001). We have studied bone mass and structure alterations in bone marrow biopsies after SCT.Patients and Methods: 67 patients after allogeneic SCT were included in this analysis. Median age was 36 years (range 17–56), 35 male, 32 female. Diagnoses were: ALL 27 patients, AML 14, MDS 6, CML 20. 38 patients were in 1. CR or 1. cP, 29 were transplanted with advanced disease. 64 received standard high-dose conditioning and 3 were transplanted after reduced intensity conditioning. 42 received bone marrow and 25 mobilized peripheral blood as stem cell source.40 patients were transplanted from HLA-identical related and 27 from unrelated donors.31 bone marrow biopsies underwent Micro-CT (Scanco, Zürich, CH) and were analysed after 3-D reconstruction. Usual parameters of trabecular structure were investigated.Results: Median bone volume/tissue volume (BV/TV), which serves as a parameter of histopathologic bone mass was 13.7% before SCT (range 8.6–44.4%), well below 18%, which are considered the osteopathologic threshold for osteoporosis. At first follow-up 6–9 months after SCT, BV/TV had dropped to 10.1% (5.9–24.6%) and at 1–2 years after SCT BV/TV was still below the pre-SCT values at 12.2% (6.1–19.3%).Number of trabecules (Tb.N.) dropped from 1.63/mm (range 0.93–2.32/mm) to 1.34 (1.01–5.61/mm) after 6–9 months and slightly increased to 1.54 (1.26–1.88/mm) after 1–2 years.Trabecular thickness (Tb. Th.) fell from 0.20 mm before SCT (normal Tb. Th. 0.20–0.30 mm) (range 0.16–0.49 mm) to a minimum of 0.16 mm (0.14–0.25 mm).As a consequence, intertrabecular space (Tb.Sp., normal appx. 0.60 mm) increased from 0.60 mm (0.36–1.11 mm) to 0.73 mm (0.23–1.04 mm) after SCT.Discussion: Independently from underlying diagnosis trabecular parameters changed within the first 6 months after SCT, indicating early loss of bone mass and structure. Afterwards, they showed some tendency to normalization, however, none of the parameters went back to baseline values. Number of patients analysed over time was to small to find out causative clinical parameters like chronic GvHD. Radiologic bone density was available for these patients and showed synchronous variations over time.Conclusions: Structural changes of trabecular bone develop early after allogeneic SCT and underscore the severeness of bone loss observed in these patients. Even after prolonged follow-up, structural changes and diminished bone mass persist and indicate a long-term cause of morbidity in these patients.

Structural Analysis of Trabecular Bone of the Proximal Femur Using Multislice Computed Tomography: A Comparison with Dual X-Ray Absorptiometry for Predicting Biomechanical Strength In Vitro

We investigated whether trabecular microstructural parameters determined in multislice spiral computed tomographic (MSCT) images of proximal femur specimens differed in male and female donors and improved the prediction of biomechanical strength of the femur compared to bone mineral density (BMD) and content (BMC) determined with dual X-ray absorptiometry (DXA) as the standard diagnostic technique. Proximal femur specimens (n = 119) were harvested from formalin-fixed human cadavers (mean age 80 +/- 10 years). BMD was determined using DXA. Trabecular microstructural parameters (bone volume fraction, fractal dimension, and trabecular thickness, spacing, and number) were calculated in MSCT-derived images of the proximal femur. Failure load (FL) was measured using a biomechanical side-impact test. An age-, height-, and weight-matched subgroup (n = 54) was chosen to compare male and female donors. BMC, BMD, and structural parameters correlated significantly with FL, with r up to 0.75, 0.71, and 0.71, respectively. In a multiple regression model, an increase up to r = 0.82 was obtained when combining trabecular structural parameters and BMC. BMD differed between males and females only at the trochanter. BMC showed significant gender differences in all regions. This experimental study showed that a combination of BMC and microstructural parameters could improve the prediction of FL, suggesting that bone mass and trabecular structure carry overlapping but complementary information and that a combination of the two provides the best prediction of bone strength. Male donors had larger femora even after adjustment for body size and height, but no differences in trabecular structure were found between males and females.

Evaluation and Development of Automatic Two-Dimensional Measurements of Histomorphometric Parameters Reflecting Trabecular Bone Connectivity: Correlations with Dual-Energy X-Ray Absorptiometry and Quantitative Ultrasound in Human Calcaneum

In osteoporosis, bone fragility results from both bone loss and changes in trabecular microarchitecture, which can be quantified by bone histomorphometric parameters. Twenty human calcaneum were collected after necropsy. All measurements were performed at the same anatomical location. Bone histomorphometric parameters were measured on histological slides with an automatic image analyzer. The aims of our study were (1) to develop automatic measurements of four additional parameters reflecting trabecular network connectivity and complexity, i.e., trabecular bone pattern factor (TBPf), Euler number/tissue volume (Euler) according to the three definitions previously reported and to a fourth one established in the laboratory (Euler(strut.cavity)), marrow star volume, and interconnectivity index, and to determine their usefulness in microarchitecture characterization; and (2) to validate these parameters by evaluating their relationship with dual-energy X-ray absorptiometry and quantitative ultrasound (QUS) measurements performed on the same samples. The statistical analysis showed that TBPf and Euler(strut.cavity) appeared to be the most significant connectivity parameters, independently of bone quantity (bone mineral density, apparent density, cancellous bone volume). For QUS, after adjustment for bone quantity, only speed of sound (SOS) was significantly and negatively correlated to Euler(strut.cavity). Broadband ultrasound attenuation depends only on bone quantity. In conclusion, TBPf (a strut analysis parameter extrapolable in three dimensions) and Euler(strut.cavity) (the only bone connectivity parameter reflecting SOS) are two valid bone microarchitecture parameters. These new parameters were significantly correlated to the established trabecular structure parameters: trabecular thickness or trabecular spacing, being weakly correlated with SOS.

Tail suspension induces bone loss in skeletally mature mice in the C57BL/6J strain but not in the C3H/HeJ strain.

We assessed the effects of tail-suspension in two skeletal genetic backgrounds, the high C3H/HeJ (C3H) and low C57BL/6J (B6) bone masses inbred mice (male, 4-months old). Cancellous bone mass and structural parameters were evaluated in distal femoral metaphysis by three dimensional microcomputed tomography. Bone cellular activities were evaluated by histomorphometry and measurements of alkaline phosphatase activity (ALP) and osteocalcin in blood and deoxypyridinoline (D-pyr) in urine. In C3H mice, 2- and 3-week unloading experiments were performed. After an early and transient decrease in body weight, a 2-week suspension period resulted in stimulation of both bone formation rate by 45% and active osteoclastic surfaces by 19%. D-pyr did not change, but ALP and osteocalcin levels increased by 18% and 72%, respectively, in 2-week suspended mice, and osteocalcin remained elevated by 30% in the 3-week suspended mice. Such cellular modifications allowed the C3H mice to maintain their initial bone mass and trabecular structural parameters even after a 3-week suspension period. In B6 mice, 1- and 2-week unloading experiments were performed. Tail suspension resulted in decreased body weight during the first days followed by an incomplete recovery during the second week of unloading. The resorption activity was unaffected by any suspension time period, whereas a decrease of 42.5% in bone formation rate and of 21.5% in ALP were seen by the end of the first week of suspension, both values being restored after a 2-week suspension period. At this latter time, trabeculae were thinner, leading to a 24.5% cancellous bone loss. Trabecular number and connectivity, rod-plate index, and degree of anisotropy were not modified. We concluded that C3H mice constituted a unique model in which genetic background overwhelmed the usual effects of reduced biomechanical usage in bone, whereas B6 mice, compared with the standardized rat model, offered an alternative model of bone loss in a mature skeleton.

Trabecular microstructure and surface changes in the greater tuberosity in rotator cuff tears.

When planning surgery in patients with rotator cuff tear, strength of bone at the tendon insertion and trabecular bone structure in the greater tuberosity are usually taken into consideration. We investigated radiographic changes in bone structure of the greater tuberosity in rotator cuff tears. Twenty-two human cadaveric shoulders from subjects ranging from 55 to 75 years of age were obtained. The integrity of the rotator cuff was examined by sonography to determine if it is intact without any tear, or torn partially or completely. The humeral head was sectioned in 3 mm thick coronal slab sections and microradiographed. After digitization of the microradiographs and imaging processing with in-house semi-automated image processing software tools developed using software interfaces on a Sun workstation, the trabecular histomorphometrical structural parameters and connectivity in the greater tuberosity were quantified. The degenerative changes on the surface of the greater tuberosity were interpreted blindly by 2 independent readers. Among the 22 shoulder specimens, the rotator cuff was found intact in 10 shoulders, partially in 7 and fully torn in 5. Statistically significant loss in apparent trabecular bone volume fraction, number of trabecular nodes, and number of trabecular branches, and a statistically significant increase in apparent trabecular separation and number of trabecular free ends were found in the greater tuberosity of the shoulders with tears. The loss was greater in association with full tear than in partial tear. Thickening of the cortical margin of the enthesis, irregularity of its surface, and calcification beyond the tidemark were observed in 2 (20%) shoulders with intact rotator cuff, in 6 (86%) shoulders with partial tear, and in 5 (100%) shoulders with full tear. Rotator cuff tears are associated with degenerative changes on the bone surface and with disuse osteopenia of the greater tuberosity. Aging, degenerative enthesopathy of the supraspinatus tendon, and rotator cuff tears appear closely related.

Stage-dependent changes in trabecular bone turnover and osteogenic capacity of marrow cells during development of type II collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is a disease characterized by inflammatory polyarthritis leading to destruction of the joints and reduction in bone mass. However, the relationship between bone mass and turnover is not yet clear in RA patients. To clarify the effect of bone turnover and marrow osteogenic capacity on mass and structure during the development of arthritis, we examined DBA1/J mice for 8 weeks after the first immunization with bovine type II collagen at the age of 9 weeks. Localized arthritis developed at 4 weeks and advanced arthritis at 6 weeks postimmunization. Urinary deoxypyridinoline levels in arthritic mice were significantly higher at 4 weeks, and levels were maintained thereafter. Their serum osteocalcin levels were significantly reduced compared with controls at 2 and 6 weeks, but did not differ significantly from those in the control group at 4 and 8 weeks. Three-dimensional (3D) trabecular bone volume of the proximal tibia measured by 3D microcomputed tomography (micro-CT) in the arthritic mice became significantly lower at 4 weeks and decreased further at 6 weeks compared with controls. Parameters of 3D trabecular bone structure, such as structure model index and trabecular bone pattern factor, were increased at 4 and 6 weeks, respectively. Trabecular osteoclast number increased and bone formation rates decreased at 8 weeks. The number of total bone marrow cells (BMCs), adherent stromal cells, and area of mineralized nodule formation in the tibia of arthritic mice were significantly reduced compared with controls at 6 weeks. Numbers of total fibroblastic colony-forming units (CFU-f) and alkaline phosphatase (ALP)-positive CFU-f colonies also decreased. However, the values of these osteogenic parameters corrected for the total BMCs and/or adherent stromal cells did not differ significantly between the arthritic and control groups. These data indicate that an increase in bone resorption led to the reduction in trabecular bone mass and deterioration of 3D structure during the localized arthritic stage. The reduction in bone marrow osteogenic potential in the advanced arthritic stage was due to the reduction in the number of total bone marrow cells, and differentiation of osteogenic cells was apparently unaffected. The reduction in bone formation may not be substantial in this arthritic model.

Disruption of the p53 gene results in preserved trabecular bone mass and bone formation after mechanical unloading.

We tested the hypothesis that mechanical unloading facilitates signaling of p53, an important modulator of cell cycling and apoptosis, in bone marrow cells and thereby reduces trabecular bone volume (BV). We performed histomorphometric analyses and bone marrow cell cultures in tail-suspended (TS) p53 null (p53-/-) and wild-type (p53+/+) mice. Eight-week-old male mice were assigned to four groups after 1-week acclimatization: p53+/+ + ground control (GC), p53+/+ + TS, p53-/- + GC, and p53-/- + TS. Bilateral tibial samples were used for analysis. The histomorphometric parameters of trabecular structure, formation and resorption did not differ between the p53-/- + GC and p53+/+ + GC groups. Trabecular BV in p53+/+ + TS mice was significantly reduced to 45% of that in the p53+/+ + GC group after one week of TS. In contrast, BV in p53-/- + TS mice was preserved at the same level as that in the p53-/- + GC group. The bone formation rate (BFR) was significantly reduced in p53+/+ + TS but not in p53-/- + TS mice. Unloading significantly increased trabecular osteoclast number (Oc.N) and surface in p53+/+ + TS mice compared with the p53+/+ + GC group, but the difference was not significant between p53-/- + TS and p53-/- + GC mice. In bone marrow cell culture, the numbers of alkaline phosphatase-positive (ALP+) colony-forming units fibroblastic (CFU-f) and mineralized nodules were significantly reduced in p53+/+ + TS, but not p53-/- + TS mice. [3H]thymidine incorporation into bone marrow cells was higher in p53-/- mice than in p53+/+ mice, independent of mechanical loading or unloading. Flow cytometric cell cycle analysis revealed that unloading significantly increased the percentage of hypoploid bone marrow cells in p53+/+ mice relative to that in p53+/+ + GC mice, but there was no significant difference in ploidy between p53-/- + TS and p53-/- + GC mice. Expression levels of p53 and p21 mRNAs were enhanced after TS in bone marrow cells from p53+/+ mice. Our data show that trabecular bone mass and bone formation were preserved after tail-suspension in p53-/- mice, closely associated with ALP+ CFU-f and mineralized nodule formation in marrow cultures obtained from tibias of p53-/- mice. We speculate that bone loss due to mechanical unloading may be related to facilitation of intracellular p53-p21 signaling.

The effect of an osteolytic tumor on the three-dimensional trabecular bone morphology in an animal model.

To investigate the application of micro-computed tomography (microCT) for the assessment of density differences and deterioration of three-dimensional architecture of trabecular bone in an experimental rat model for tumor-induced osteolytic defects. Walker carcinosarcoma 256 malignant breast cancer cells (W256) were surgically implanted into the medullary canal of the left femur of 15 4-month-old rats. Twenty-eight days after surgery all animals were killed and both femora from each rat were harvested. A total of 30 specimens (left and right femur) were scanned in a desktop microCT imaging system (microCT 20, Scanco Medical) to assess densitometric and architectural parameters. For each specimen a total of 200 micro-tomographic slices with a resolution of 30 microns in the distal metaphysis was taken. Bone mineral content (BMC) was analyzed for both cortical and trabecular bone (ctBMC), and for trabecular bone only (tBMC). Architectural indices (BV/TV, Tb.N, Tb.Th, Tb.Sp) according to standard definitions used in histomorphometry were calculated for trabecular bone. The quantitative analysis of density parameters revealed significantly (P < 0.001) lower values for ctBMC and tBMC in the tumor-bearing group (T) of 26% and 31%, respectively, compared with the contralateral control group. The quantitative analysis revealed significant (P < 0.001) changes in the architectural parameters in the tumor-bearing bones compared with the contralateral control group: BV/TV was 30% lower, Tb.N and BS/TV decreased by 24% and 21%, respectively, Tb.Th. decreased by 10% and Tb.Sp. increased by 94%. This study demonstrates that microCT is able to provide three-dimensional parameters of bone mass and trabecular structure in an animal model for tumor-induced bone loss. Recent advances in therapeutic approaches for skeletal diseases such as osteoporosis and metastatic bone diseasse rely on an understanding of the effects of the agents on the mechanical properties of bone. In order to quantify the structural changes of the affected bones the application of a non-destructive method is mandatory. The use of microCT seems to be a great advantage, since biomechanical tests and further histologic analysis can be done for the same specimens.

Trabecular bone mineral and calculated structure of human bone specimens scanned by peripheral quantitative computed tomography: relation to biomechanical properties.

The relationship of cortical bone mineral density (BMD), and geometry to bone strength has been well documented. In this study, we used peripheral quantitative computerized tomography (pQCT) to acquire trabecular BMD and high-resolution images of trabeculae from specimens to determine their relationship with biomechanical properties. Fifty-eight human cubic trabecular bone specimens, including 26 from the vertebral bodies, were scanned in water and air. Trabecular structure was quantitated using software developed with Advanced Visual Systems interfaced on a Sun/Sparc Workstation. BMD was also obtained using a whole-body computerized tomography scanner (QCT). Nondestructive testing of the specimens was performed to assess their elastic modulus. QCT and pQCT measurements of BMD of specimens in water were strongly correlated (r2 = 0.95, p < 0.0001), with a slope (0.96) statistically not significantly different from 1. Strong correlations were found between pQCT measurements of specimens in water and in air, for BMD (r2 = 0.96, p < 0.0001), and for apparent trabecular structural parameters (r2 = 0.89-0.93, p < 0.0001). Correlations were moderate between BMD and apparent trabecular structural parameters (r2 = 0.37-0.64, p < 0.0001). Precision as coefficient of variation (CV) and standardized coefficient of variation (SCV) for these measurements was < 5%. For the vertebral specimens, the correlation was higher between elastic modulus and BMD (r2 = 0.76,p < 0.0001) than between elastic modulus and apparent trabecular structural parameters (r2 = 0.58-0.72, p < 0.0001), while the addition of apparent trabecular nodes and branches to BMD in a multivariate regression model significantly increased the correlation with the elastic modulus (r2 = 0.86, p < 0.01). Thus, pQCT can comparably and reproducibly measure trabecular bone mineral in water or air, and trabecular structure can be quantitated from pQCT images. The combination of volumetric BMD with trabecular structural parameters rather than either alone improves the prediction of biomechanical properties. Such a noninvasive approach may be useful for the preclinical study of osteoporosis.